Surface chemistry means the instigation of chemical reactions upon or within surfaces. In the former case, growth of thin films or inactivation of organic matter, such as bacteria or its byproducts known as pyrogens, is known to occur using ion or electron beams, usually at low pressure. In the latter case, certain surfaces, such as silicon, can be converted to oxides with surface reactions. An example of such conversion is the conversion of the surface of a silicon wafer to silicon dioxide by introducing a reactive oxygen species near the wafer surface, usually in vacuum.
In U.S. Pat. No. 5,508,075 A. Roulin et al. disclose formation of an oxygen barrier layer on a surface as a packaging laminate. A plasma is formed in a vacuum chamber in order to carry out plasma enhanced chemical vapor deposition (PECVD). Organic silicon compounds are combined with oxygen within the plasma such that the two compounds react and are deposited upon and chemically bonded to the surface. Silicon oxide can be formed directly on the surface. The patent indicates that preferred substrates or surfaces are flexible thermoplastic materials.
It is known that electron beams are useful for surface treatments. In U.S. Pat. No. 5,909,032 G. Wakalopulos discloses an arrangement of electron beam tubes which produce a linear or stripe-like electron beam suitable for surface treatment. The Wakalopulos patent features electron beam tubes which are sealed vacuum tubes emitting a beam through a thin window into an ambient environment, such as air, a relatively high pressure environment compared to the vacuum environment of the interior of the tube where the electron beam is generated. The construction of the Wakalopulos tube is shown in U.S. Pat. Nos. 5,637,953 and 5,414,267, both assigned to the assignee of the present invention.
The above mentioned beam tubes produce electron beams which interact with air, causing ionization of the air, creating secondary electrons which participate, together with the primary electrons of the beam, in surface treatment. One of the problems which is encountered is that the beam is evanescent, quickly become neutralized. Since the beam is continuous, the evanescent nature of the beam is not important for some applications. In other applications, a more persistent beam is needed to achieve the desired effect.
Electron beams have previously been used for sterilization. However, in many cases a residue of proteinaceous material is left because microorganism debris tenaciously adheres to a surface. The disabling of the microorganism does not necessarily disable the chemical bonds retaining the microorganism to a surface.
An object of the invention was to devise a high pressure electron beam tube apparatus with a persistent beam for surface sterilization, and a sustainer discharge for inactivation of proteinaceous material from treated surfaces.
Another object of the invention was to devise a high pressure plasma apparatus for chemical vapor deposition, grafting, and in particular thin film formation.